Flow gauges for central heating pipe work

[doitmyself]

If you require 20 LPM without any piping alterations and if your water supplier was willing then because flow is proportional to the square of pressure,

NO. Flow rate is approximately proportional to the square root of the pressure difference between the two ends of the pipe. So, assuming the open end is at atmospheric pressure and the supply end is at 1 bar above atmospheric, increasing the supply to 2 bar above would only increase the flow rate by √2, i.e. 1.414 times, not by 4 times which you are suggesting.

 

[John.g]

NO. Flow rate is approximately proportional to the square root of the pressure difference between the two ends of the pipe. So, assuming the open end is at atmospheric pressure and the supply end is at 1 bar above atmospheric, increasing the supply to 2 bar above would only increase the flow rate by √2, i.e. 1.414 times, not by 4 times which you are suggesting.

Quite correct, I should have stated that pressure is proportional to the square of the flow, so as my figures suggested, if the supply end was 1 bar then to increase the flow from 12 LPM to 20 LPM would require a supply end pressure of 2.78, ((1*(20/12)^2.)

 

[chris watkins]

NO. Flow rate is approximately proportional to the square root of the pressure difference between the two ends of the pipe. So, assuming the open end is at atmospheric pressure and the supply end is at 1 bar above atmospheric, increasing the supply to 2 bar above would only increase the flow rate by √2, i.e. 1.414 times, not by 4 times which you are suggesting.

Quite correct, I should have stated that pressure is proportional to the square of the flow, so as my figures suggested, if the supply end was 1 bar then to increase the flow from 12 LPM to 20 LPM would require a supply end pressure of 2.78, ((1*(20/12)^2.)

And the practical application of all this higher level math is what may I ask ?
I love to learn but have to understand what it can do for me have you any examples for a lonely plumber or heating engineer, please?

 

[Jones82]

Just reading some interesting articles on pumps and understanding them further. It seems quite common, on an industrial scale, as a previous poster mentioned, to position gauges "on the suction" side of the pump and "on the discharge" side of the pump. I might buy a couple of low ranging gauges and experiment with them on my own system.

It does seem that a pressure gauge is the way to go.

Its odd that boilers measure flow rate, as we've mentioned, using electrical sensors, they then use this information to modulate accordingly. However an electronic flow sensor hooked up to a digital display doesn't seem to exist?

I had an ideal engineer out to a boiler recently. He hooked up his laptop and the flow sensor reading was displaying on his software.... So the technology exists but perhaps just isnt on the market?

 

[John.g]

I would venture that the ideal engineer was picking up that info on a App on his laptop linked to the circulating pump.
Grundfos have a Alpha 3 Model B 15-50/60 (6M pump) which you can link to your laptop/smart phone with the grundfos go App and from what I can see its a pandora's box of info/settings.
I don't know what boiler type/pump location you have but if its a externally mounted pump then you might consider installing one of these pumps or something much more down market (and cheaper) like my pump which is a Wilo Yonos Pico 1-6 (6M pump) which has plenty of settings but only then displays the power in watts while running but you can then derive the flow rate and the pump head from its pump curves quite easily.
I think you would learn far more from something like this rather than just installing two pressure gauges.
Incidentally, what make/model pump have you installed, it may already be a "smart" A rated pump which may already display the power.

Edit: Some more info here which may be of interest:
How to choose the correct speed control for heating systems - Lowara - International

 

[Jones82]

It was a grundfos 25-80, beast of a pump, think it was 20 litres a min on his laptop but the pump just had the usual 3 settings, it didn’t display watts.

Also I suppose it’s not really the performance of the pump I’m interested in. I’m interested in the performance of the system.

So how much force is the pump generating and how much is lost going round the various pipe runs.

I realise we could work this out on paper if we knew every bend and pipe run but in reality it’s either impossible or just too much grief!

So back to the original premise. Is there a way of measuring the frictional resistance of a heating system using gauges / flow meters / electronic sensors?

 

[doitmyself]

Some more info here which may be of interest:
How to choose the correct speed control for heating systems - Lowara - International

Very informative. The bit about constant pressure and underfloor heating confirms what I had read in some Grundfos literature - not that I can find it now. I guess that would also apply to microbore systems where the rads are fed, individually, from a manifold.

The other bit which struck me was the statement that current high efficiency pumps "are seriously lacking in sensory input. They can detect the system resistance and, if they have a built-in temperature sensor, they can detect system temperature." This means that all the "data" which is presented by the Grundfos Alpha 3 App is derived (from frequency, current etc?), not measured directly. I have read criticisms of the Alpha 3 that the data is not always accurate.

 

[John.g]

Yes, all these pumps derive the head and flow from the power (easily measured), the frequency (again easily measured) BUT they must also know the pump&motor efficiency at every point on every curve setting, which is literally hundreds of "numbers" as a lot of these pump's PP and CP settings can be increased from say 0.5M to 6M in 0.1M increments, I would love to know how this is done (efficiency calculations). I used my (oil) boiler rated output and the measured deltaT to calculate the flow rate and it compared within 10% of the derived flow from the Wilo power so I suppose fair enough for most purposes.

 

[John.g]

It was a grundfos 25-80, beast of a pump, think it was 20 litres a min on his laptop but the pump just had the usual 3 settings, it didn’t display watts.

Also I suppose it’s not really the performance of the pump I’m interested in. I’m interested in the performance of the system.

So how much force is the pump generating and how much is lost going round the various pipe runs.

I realise we could work this out on paper if we knew every bend and pipe run but in reality it’s either impossible or just too much grief!

So back to the original premise. Is there a way of measuring the frictional resistance of a heating system using gauges / flow meters / electronic sensors?

I'm afraid I can,t give a really meaningful answer to the above, apart from saying that it is physically possible to fit differential pressure and flow gauges to every loop in the system.

 

[Riley]

It’s just overkill though chaps. You are going to get joe public looking at this and thinking it’s rocket science to change a pump when it’s just not. Talk about baffling with science